TTB-9-2920-225-34-1 Regulator Check Out and Repair 100 Amp 2920-00-900-7993 Download
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TB 9-2920-225-34-1 Section II. VAP-AIR MODEL 26440001-01 2-4. General. Figures 2–3 and 2–4 show two views of the regulator and its parts. Diode and transistor NSNS and parts numbers with substitute NSNS and part numbers are listed in table 2–1. 2-5. Checkout and Repair. a. Voltage Adjustment Rheostat (R6) (power disconnected). (1) Remove voltage adjustment access plug (see fig. 2-3). (2) Place ohmmeter test probes to terminals of the rheostat (see fig. 2-3). (3) Rotate rheostat fully clockwise; reading should be less than 5 ohms. (4) Rotate rheostat fully counterclockwise; reading should be approximately 2500 ohms. (5) If other readings are obtained, replace rheostat. b. Transistors. (1) Carefully remove transistors Q7, Q8, and Q9 (see fig. 2-3). (2) Position transistor as shown in figure 2-1, and check each separately (see fig. 2-2). (3) If resistance values differ from the values shown in figure 2–2, replace the transistor ac- cording to table 2–1. NOTE Transistors Q8 and Q9 are identical and can be interchanged. Transistors Q7 must be replaced by a like item in the same socket (see fig. 2-3 ). (4) Check the mica insulating washer be- tween the transistor and mounting plate. Replace if cracked, broken, or missing. Coat washers with insulation compound per MIL-S-8660, NSN 6850– 00–880-7616. c. Diode. (1) Remove four screws holding transistor mounting plate and move plate to one side. (2) Place negative ohmmeter probe to the connector side of diode CR6 (see fig. 2–3). (3) Place positive probe to the circiut board side of CR6. Meter should indicate low resistance. (4) Reverse probes. Meter should indicate high resistance. (5) If other readings are obtained, replace diode CR6 (MR1122), NSN 5961–00-103–1519 (see fig. 2-4). (6) Reinstall transistor mounting plate. d. Circuit Board. If no faulty components were detected after performance tests a, b, and c above, replace the circuit board. e. Functional Check. Check the performance of the regulator on the test stand and make final voltage adjustments. Voltage output should read 28 volts. If the regulator does not function prop- erly, perform the following: (1) Check wires and connections. (2) Replace circuit board. (3) Perform bench test procedures. NOTE After final repair, check the test stand. If the regulator still does not regulator on function correctly it will be necessary, if local skills permit, to test each component. All the parts should be checked with an ohmmeter and the capacitors checked with a capacitance meter. The circuit board traces should be checked with an ohmmeter to make sure that there are no cracked traces. Traces with hairline cracks will show good at lower tempera- tures and will tend to show open circuit at higher temperatures. If the board seems good at room temperature, but the regulator still fails, this could be the cause. Table 2–1. Replacement Parts List—Model 01 2-3